The invention concerns a process for determining the operating point of an automatic transmission, particularly a continuously variable transmission, having means for detecting input signals which are drawn from a driver-vehicle system and are processed to at least one output signal by which, within the scope of an operating strategy, determined is the reduction ration and/or the speed of rotation of a prime mover and/or the vehicle acceleration or the like.
In the requirement profile of a driving strategy for a continuously variable transmission, the points of concern are a good driveability, a favorable consumption and an application effort acceptable in the practice. In the conversion of a driving strategy the resource requirement must be low. The driving strategy must automatically adapt to different driving situations (driver, vehicle and environment). The system must insensitively react in case of errors common in the practice, that is, it must have a certain sturdiness.
In the solution proposed in DE-A43 12415, characteristic lines are combined to form a switch characteristic field in which a limit line corresponds to a characteristic line of an optimized consumption and one other limit line to a characteristic line of optimized performance. The operating points between said limit lines lie on so-called dynamic characteristic lines, the position of which depends on the variable of the change of speed of the required performance.
In EP-A 0 657 668 two speed-dependent power limit curves are plotted as characteristic lines in the P-v diagram. With said characteristic lines associated are a minimum and a maximum evaluation number. The actual engine power is determined and compared with the two limit curves. By the comparison received are the actual evaluation numbers that are filtered. With the aid of the filtered evaluation number there determined are two-dimensional characteristic lines of three-dimensional characteristic line fields for control of the input unit.
The known process is, in partial aspects, advantageous for driving a strategy, since the actual evaluation number can be found by simple interpolation. The control of the time characteristic, via an adequate filter, must require no great effort. But, on the other hand, it remains open in the know process how other, no less important partial aspects of the requirement profile, can be taken into account.
To reduce the development time, it is proposed in the device for control of a continuously variable transmission according to DE-A 44 45 325 to evaluate the engine torque in order to calculate an input torque of the transmission. By comparing the calculated input torque of the transmission with a theoretical input shaft torque, which is based on the parameters informed of the engine load, a theoretical reduction ratio is determined. From performance graphs of theoretical input shaft torque deduced is a theoretical reduction ratio which is compared with the actual reduction ratio of the continuously variable transmission. From the difference, a controlled output is drawn in order to equate the actual reduction ratio with the theoretical reduction ratio. This solution, however, also requires several performance graphs in order to take into account an actual mode of driving.
In the device of DE-A 42 23 967 a transmission output torque is set within the scope of a predetermined operation strategy. The presettable operation strategy represents a sporting or consumption-favorable driving characteristic. A performance graph, particularly with points of support, is determined by consumption measurements. The theoretical value of the transmission ratio is selected as low as possible depending on a minimum speed of rotation of the engine and a desired output torque.
The continuously variable transmission reacts in special situations with an uneven acceleration characteristic. The subjective driveability can be objectively made clear by the following characteristic: upon a leap-like change of the throttle valve position, the theoretical speed of rotation value of the prime mover jumps vertically. Contrary to this significant increase of the engine speed of rotation, the vehicle speed remains at first constant for a certain period of time. Consequently, it is mainly disadvantageous that the driver at first notices no acceleration of the vehicle. Under unfavorable circumstances, a brief deceleration of the vehicle can occur. The driver seeks to overcome said situation by reporting a still greater need of power. The consequence of this is an over control of the throttle valve.
The problem on which this invention is based is to provide a process for determining the operating point of a continuously variable transmission which guided itself by superimposed variables, such as driver's wish, mode of driving and driving state.